1. Field of the Invention
This invention relates in general to detection circuits and in particular to peak voltage level detection circuits.
2. Description of the Prior Art
There are numerous prior art circuits whose function is to measure the level of an incoming signal. The techniques employed within such circuits to make such measurements are almost as numerous as the number of circuits. In many of these circuits, a capacitor is charged to a particular level and then this charge level is used to either trigger some other function, such as a warning of when a critical value is approaching, or for comparison to a later-received signal.
The type of devices in which such detection circuits are used controls the composition of the incoming signals which the detection circuit receives. Similarly, the particular application for the detection circuit governs the design details of the detection circuit. Following are some examples of the variations which exist in prior art detection circuits.
U.S. Pat. No. 3,548,307 issued to Fathauer discloses a circuit which is adapted for use with a variable input signal from a radar set. The circuit is used to capture a variable signal of short duration which can be held (by use of a push-button switch) thereby permitting a readable meter indication which would otherwise be too brief to accurately read.
U.S. Pat. No. 3,491,296 issued to Fishman requires that the incoming signals which are to be measured have a constant or slowly varying pulse amplitude.
U.S. Pat. No. 2,946,013 issued to Deighton relates to voltage-measuring circuits for measuring the amplitudes of voltage pulses of short duration. The circuit stores the voltage across a capacitor while the amplitude is compared with a known voltage.
U.S. Pat. No. 3,949,294 issued to Imura discloses a circuit with changeable time constant sections such that suitable rise and decay times are provided for indicating both the peak value of an audio signal and/or the resultant volume of the sound (VU indication).
U.S. Pat. No. 3,973,197 issued to Meyer discloses a circuit for detecting the positive and negative peaks of an analog signal by first converting the analog signal into a current digital signal and then comparing this signal to a previously developed and stored signal and exchanging signals to establish new stored signals.
U.S. Pat. No. 3,694,748 issued to Hekimian discloses a peak-to-peak detector circuit for measuring the voltage difference between positive and negative peaks of a signal.
Other patents which have come to my attention in connection with such detection circuits are as follows:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 2,468,687 Schmitt 4/26/49 3,790,887 Rich 2/05/74 3,753,109 Schainbaum 8/14/73 3,259,760 Morey et al. 7/05/66 3,012,195 Slocomb et al. 12/05/61 ______________________________________
Also known within the art is the use of a voltage comparator integrated circuit as part of a positive or negative peak detector circuit. A suitable integrated circuit for such use is an LM 311 available from National Semiconductor, Santa Clara, Calif.
Even with the wide variations in the prior art as to the type of circuits and their application, none of these prior art patent references disclose a circuit specifically designed to be used in conjunction with a tunable RF voltmeter or the like, which is intended for measuring signals which may be either modulated or unmodulated (CW) and to display the peak amplitude of such signals accurately, regardless of which type of carrier is present or which type of carrier was used to calibrate the deflection of a meter (used as the displaying means).
One object for any detection circuit design intended to measure a particular signal level is to be able to make such measurement accurately and with reliable repeatability. Past efforts in the design of tunable RF voltmeters have been unable to accurately and repeatedly indicate a level proportional to the peak amplitude of an incoming signal as this signal changed between a modulated and a CW (unmodulated) waveform. If the displaying meter was calibrated by a modulated signal, the measurement of a subsequent unmodulated signal would be subject to significant error.